Conservation agriculture influences soil nitrogen availability in the lower Indo-Gangetic Plains

Information on the effect of conservation agriculture (CA) on N availability in soil is inconsistent. Estimation of available N using conventional analytical methods may not be suitable due to changes in N forms in soils under CA. The study aimed to assess the impact of CA on N availability in soil and to evaluate estimation methods for plant-available N under CA.

A field experiment was conducted involving fifteen treatments comprising three tillage operations and five rice residue + nutrient management practices with three cropping systems [rice-maize-cowpea (RMaC), rice-mustard-black gram (RMuB) and rice-cauliflower-rice (RCR)] in alluvial soils of the lower Indo-Gangetic Plains. Availability of N in surface soil layers was assessed using neutral phosphate buffer (PB), calcium chloride (CC), sodium bicarbonate (SB) and alkaline permanganate (PP) methods after three years.

The amount of available N extracted by the four methods followed the order SB > PB > PP > CC. Zero tillage with 50%residue + 100%NPK and 100%residue + 75%NPK resulted in ~ 3 to 20% and 3 to 12%, respectively, higher available N in soils over other CA treatments for RMaC and RMuB cropping systems. In contrast, reduced tillage with 50%residue + 100%NPK had ~ 1 to 13% higher available N for RCR cropping system.

This work offers choice of efficient CA practices with higher plant available N in soils. Novel multi-criteria-based technique identified PB as the best method in estimating available N in soils under CA with rice-based cropping systems.